1. Field of the Invention
The present invention relates in general to systems for testing internal connectivity in Asynchronous Transfer Mode (ATM) switching equipment, and more particularly, to a system for testing internal connectivity within an ATM switching system by sending and receiving loopback OAM cells.
2. Description of the Related Art
For efficient and reliable operations and maintenance of ATM networks, the International Telecommunication Union-Telecommunication Sector (ITU-T) has formulated a network management scheme using OAM cells, where the term xe2x80x9cOAMxe2x80x9d stands for operations, administration, and maintenance. Loopback function, one of the key test capabilities provided in this scheme, uses loopback OAM cells to verify the connectivity between any two points in an ATM network.
According to the ITU-T Recommendation I.610, the loopback OAM cell has a field called xe2x80x9cloopback location ID fieldxe2x80x9d to address a specific ATM switching system at the endpoint of a connection or a segment under test, as the loopback point. Upon receiving such a loopback OAM cell through a certain physical link, each ATM switching system compares its own identifier with the loopback location ID field value of the received cell. If they coincide with each other, then the ATM switching system sends the received loopback OAM cell back to the same physical link, allowing the connectivity between the originator and the endpoint node to be verified.
Consider a situation that the ATM network encountered trouble and the connectivity test has been conducted subsequently by using loopback OAM cells to investigate the point of failure. This test can indicate which ATM switching system is faulty; however, it is unable to tell which internal subsystem or component is defective in that ATM switching system.
To test whether the ATM cells are being relayed properly by each part of the target ATM switching system, it is necessary to establish some dedicated test channels or newly define some special cells for this purpose. However, such dedicated test channels would lead to the degradation in service quality, because it consumes some channels and thus reduces the network bandwidth available to users. The use of special test cells, on the other hand, needs efforts to revise the relevant standards to introduce new definitions, and also requires additional software development so that the existing ATM switches will be able to handle the new cells in conformity with the standards.
Taking the above into consideration, an object of the present invention is to provide a system which can test the internal connectivity in an ATM switching system without establishing any dedicated channels or using special cells for the test purposes.
To accomplish the above object, according to the present invention, there is provided a system for testing internal connectivity in an ATM switching system by using loopback OAM cells, where the ATM switching system contains a plurality of local subsystems. This system comprises: a transmission unit which transmits a loopback OAM cell containing a local subsystem identifier in a predetermined field thereof to indicate one of the local subsystems constituting the ATM switching system; and a response unit, disposed in each local subsystem and activated when the loopback OAM cell is received from the transmission unit, which returns the received loopback OAM cell if the identifier found in the predetermined field of the received loopback OAM cell agrees with the local subsystem""s own identifier.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.